Effect of gelling on the impedance parameters of Pb/PbSO4 electrode in maintenance-free lead-acid batteries

The impedance parameters of Pb/PbSO4 electrode in 4.8 M sulfuric acid have been measured potentiostatically under open-circuit conditions over a wide range of frequencies (10(-2) to 10(4) Hz) under both deep-discharged (state -of-charge, SoC = 0) and fully charged (SoC = 1) conditions. Immobilization of the electrolyte by adding sodium silicate (5 g/l) on the impedance of P b/PbSO4 electrode shows significant difference in comparison with the flood ed system. Four equivalent circuits have been formulated for overcharged an d deep-discharged electrodes in gelled and flooded electrolytes, respective ly. Impedance parameters are calculated using a phenomenological model, whi ch indicates that in the case of gelled electrolytes, the electrochemical r eactions are mass-transfer controlled, in contrast to the flooded electroly te cells, where the process is known to be charge-transfer controlled. The study provides a non-destructive investigation of the effect of gelling on the electrical performance of sealed maintenance-free lead-acid batteries. (C) 2000 Elsevier Science S.A. All rights reserved.